"I could certainly foresee circumstances in which we would not want imagery to be openly disseminated of a sensitive site of any type, whether it is here or overseas."

The NGA has actually been more of a military mapping bureau than a movie-style satellite-using spy outfit. Its motto is "Know the Earth...Show the Way," and most of its products are more on the lines of Google Earth than live satellite monitoring of people or individuals.

But Murrett is a former naval intel analyst, and "NGA provides accurate, up-to-date geospatial intelligence...NGA's strategy supports operational readiness through a set of geospatial foundation data...fused with other spatially referenced information such as intelligence, weather and logistics data. The result is an integrated, digital view of the mission space".

In other words, NGA gets to look at the secret poop from the proper spies in order to put the various counters onto the big map which it has provided. So it may not be the CIA, NSA, DIA, or whoever, but it really is "a crucial member of the intelligence community", as it insists.

In particular, NGA has lately provided $1bn in funding to commercial sat-imagery operators such as Digital Globe and Geoeye. Firms such as these provide much of the imagery used by the likes of Google Earth, and Murrett is no doubt thinking of them when he talks about the US government imposing restrictions. In the case of US-based companies where the NGA controls the money, this would be a simple matter.

There are also means whereby even foreign-based providers can be muzzled. During the 2001 US-special-forces-led invasion of Afghanistan, for instance, the NGA bought up all the imagery over that country for several months, preventing anyone else from getting it. This led to a lot of criticism on the grounds that the US government was muzzling the media and hampering relief work.

Murrett clearly believes that such methods may be justified, however.

"I think we may need to have some control over things that are disseminated. I don't know if that means buying up all the imagery or not. I think there are probably some other ways you could do it," he said.

Just what other ways these might be - especially in the case of non-US organisations disseminating images from non-US satellites - was not made clear. Diplomatic pressure or international law could often be brought to bear, no doubt; and if a future US government felt the need were urgent enough it could resort to electronic/information warfare or even shooting down troublesome satellites, like the Chinese.

But it's likely that Admiral Murrett was really talking more about keeping useful commercial satellite images out of the hands of terrorist groups planning attacks on US facilities or personnel abroad. That could be quite a difficult tightrope to walk. Blanking out big areas for long periods by commercial or other means would cause a storm of complaint; narrowing the time/space curtain might risk giving away the very information one wishes to keep secret.

One thing's clear, however. Commercial satellite-imagery operators will need to tread warily in future. This is one market in which various national governments will feel a frequent need to interfere. ®